Dell Latitude 10 St2 “No bootable devices”

After an optional Windows update my tablet (I have 5 of them) would no longer get past the sign in screen, it would simply go to shut down. I entered the repair section and tried all of the options and on the complete reinstall I get an error. So I made a bootable usb to reinstall the original os and I was able to get it to work until I got the same error as before. Now the tablet will not get back to the recovery page - it is a black screen with “no bootable devices—-strike f1 to try reboot...” etc. I can still get to bios using + and - volume but I have no UEFI options any more. The diagnostics says everything is fine. If I try booting with usb in the screen just stays black with nothing happening.